1. Field of the Invention
This invention relates to audible-visual warning alarm systems.
2. Description of the Prior Art
Various visual and audible signal systems have heretofore been proposed but these have had shortcomings from the viewpoint of complexity of design, difficulty of installation, or have had maintenance problems.
McGill, in U.S. Pat. No. 3,545,272, shows a liquid level warning device responsive to a pluarlity of liquid levels to provide corresponding visual indications through vari-colored lamps. The structure shown might be useful on an instrument panel but is not suited for use out of doors or with concurrent audible signals.
Alexander, in U.S. Pat. No. 3,685,357, shows a sensor responsive to a plurality of liquid levels with signal lights of the panel type giving visual indications of the respective levels, except for an auxiliary audio signal for high liquid level. No provision is made for out of doors operation, nor for a plurality of different audible signals at different levels with one input having priority over the other.
Cromer, in U.S. Pat. No. 3,346,857, shows plural tone audible indicating apparatus responsive to different liquid levels with repetitive changes from one tone signal to the other controlled by a free running multivibrator. The signals are intended to be connected to a telephone line for interpretation through normal hearing by means of a conventional telephone instrument at a remote point.